Warning: SPOILERS for The Batman and Joker.
The Batman wastes the opportunity to crossover with Joker by introducing Barry Keoghan as an in-universe Joker. The reveal of Keoghan as the Joker in Matt Reeves' Batman universe is undeniably exciting, but the Gotham the director crafted is so similar to the city of Todd Phillips' Joker, it seems a shame that the two franchises will not cross over. While Keoghan will no doubt prove a fascinating portrayal of the iconic Batman villain, the concept of Pattinson's Batman interacting with Joaquin Phoenix's Joker was one with a lot of potential, which is now ultimately wasted.
Joker introduces Arthur Fleck, a mentally ill party clown who eventually transforms into the villainous Joker in a version of Gotham City based on New York City in 1981. The film also sees him cross paths with Thomas and Martha Wayne, and he even meets their young son, Bruce. When Arthur starts a riot, a thug ends up killing the Waynes in Crime Alley. In contrast, The Batman takes place in a modern setting, following an adult Bruce Wayne in his first years of being Batman. He takes down the Riddler, who ends up meeting a different version of the Joker in Arkham Asylum. A deleted scene also shows Batman consulting this Joker for hints on how to catch the Riddler.
Introducing a new version of the Joker when Phoenix's version seems rife for a crossover is a mistake. Though the two films are set in different time periods, the year is never specified in The Batman, and this could easily be written around. Logistically speaking, if Keoghan's Joker was not revealed in the deleted scene and the actor identified, the door still could have remained open for Phoenix to crossover into Reeves' Batman universe, which would have generated further interest in the franchise, while also making sense for both films and their respective universes.
The tones of both The Batman and Joker are very similar, and they present an equally pessimistic view of Gotham City. It is easy to imagine Arthur Fleck roaming the streets of the Gotham of The Batman, resenting the elite in much the same way the Riddler does. Furthermore, seeing a confrontation between two major powerhouse actors like Robert Pattinson and Joaquin Phoenix would be a genuine treat for audiences, and an opportunity unlikely to arise in any other film.
Of course, there is still a chance that Keoghan's Joker could actually be the link between the two films. A theory suggests that Arthur Fleck may not be the Joker himself (due to being much older than Bruce and lacking his comic book origin), but merely his inspiration. With the period difference and the fact that Barry Keoghan's Joker appears scarred and burned - hinting at his fall into a vat of acid - a crossover with Joker could still prove this theory true.
It is very unlikely that Joaquin Phoenix will appear in a sequel to The Batman, given the amount of hype around Barry Keoghan's version of the character. Though Arthur Fleck could prove an interesting theory true, it seems that Reeves wants to craft his own vision of the Clown Prince of Crime, without relying on Todd Phillips' version from Joker. It's a shame, as seeing Pattinson and Phoenix go head-to-head would have been compelling, even if Reeves would need to write around the plot holes their confrontation would inevitably present.
